The present invention relates to an atomic absorption spectrophotometer using a graphite cuvette (namely, an absortion cell made of graphite), and more particularly to an atomic absorption spectrophotometer which can accurately detect the temperature of the graphite cuvette used.
In an atomic absorption spectrophotometer using a graphite cuvette, a metallic element contained in a sample is atomized by heat from the graphite cuvette, and measuring light from a hollow cathode lamp is selectively absorbed by the atomized metallic element. Thus, the metallic element can be quantitatively determined on the basis of the measured absorbance. In more detail, the measuring light from the hollow cathode lamp passes through the graphite cuvette and is then led to a spectroscope through an optical element (that is, a mirror or lens), to extract only a wavelength component which can be absorbed by the metallic element. Further, an electric current is supplied to the graphite cuvette, to heat and atomize the sample with the aid of the Joule heat which is generated in the graphite cuvette. In such an operation, the reproducibility of an increasing rate of graphite sample atomizing temperature have a great influence on the result of analysis, and hence it is required to detect the temperature of the graphite cuvette accurately. A temperature control device has been proposed in U.S. Pat. No. 4,283,934. In this device, a detector is disposed in the vicinity of a graphite cuvette (namely, a graphite tube) to detect the thermal radiation from the graphite cuvette, and a current supplied to the graphite cuvette is changed in accordance with the output of the detector, to set an atomizing temperature to a desired value. In the above device, however, when the sample is heated and atomized, the detector is contaminated with various substances from the graphite cuvette, since the detector is disposed in the vicinity of the graphite cuvette. That is, the detector is contaminated with the vapor of the sample, or the vapor of an acid, alkali, or others contained in the sample. Further, carbon powder is scattered from the graphite cuvette, and deposited on the detector. That is, the detector is contaminated with the carbon powder. Such contamination proceeds with time, and reduces the transmissivity of the light receiving surface of the detector. Thus, it is impossible that the detector receives the radiation from the graphite cuvette correctly, and the correctness of temperature control is lost with time.